1. Field of the Invention
This invention relates to novel polymeric whitening agents which contain at least one fluorescent monomer component and one hydrophilic monomer component. The polymeric whitening agents may optionally contain a hydrophobic monomer component. The polymeric whitening agents may be used in fabric care compositions and provide enhanced fluorescence when used on hydrophilic and/or hydrophobic substrates.
2. Prior Art
Conventional fluorescent whitening agents (FWAs) for textiles have been used for many years as optical brighteners for fabric. These materials function by replacing the blue-violet component of visible light depleted by chromophore-containing soils in the form of blue fluorescence. This replacement reduces and/or eliminates the yellow tinge cast onto dingy fabrics by completing the full complement of visible light colors, leading to white light with a brightening effect.
FWAs currently used in detergent formulations are generally sulfonic acid salts of diaminostilbene derivatives such as those taught, for example, in U.S. Pat. No. 2,784,220 to Spiegler or U.S. Pat. No. 2,612,501 to Wilson. FWAs of this type have been long known to significantly "whiten" cotton. However, their brightening effect on less hydrophilic fabric, especially aged cotton, is substantially reduced. The most likely explanation for this phenomenon is that, while sulfonic acid salts of diaminostilbene fluorescent whitening agents are able to hydrogen bond to hydroxyls on the surface of cellulose via the sulfonate anion - hydroxyl proton hydrogen bonding interaction, this effect is reduced in polyester/cotton blends and is altogether absent in pure polyester. In the case of soiled cotton, oily soil residue can hydrophobically modify the surface of cellulose, deterring the deposition of hydrophilic FWAs.
It has been demonstrated that poly(ethylene terephthalate)/poly(oxyethylene terephthalate) copolymers adsorb onto hydrophobic surfaces to confer soil release properties. See U.S. Pat. No. 4,702,857 to Gosselink; U.S. Pat. No. 4,569,772 to Ciallela; and U.S. Pat. No. 3,959,230 to Hays. These materials are believed to function by hydrophilically modifying a hydrophobic surface (such as oily soil on fabric or polyester fabric itself), and thereby deterring deposition of hydrophobic soils. The poly(ethylene terephthalate) unit is believed to seek and adhere to the hydrophobic surface; the poly(ethylene glycol) portion is believed to give hydrophilic character to the fabric surface as well as aid the polymer in transfer through the aqueous medium. None of these references teach or suggest the use of a copolymer comprising a hydrophilic portion (capable of delivering the copolymer through an aqueous system) and a fluorescent portion (capable of simultaneously altering optical properties and serving as an anchoring group to provide substantivity for the hydrophobic agent).
U.S. Pat. No. 4,739,033 to Morris et al; U.S. Pat. No. 4,728,720 to Morris et al. and U.S. Pat. No. 4,720,719 to Morris et al. teach that 4,4'-stilbenedicarboxylic acid can be copolymerized with aliphatic diols to give materials with good mechanical properties and chemical resistance. U.S. Pat. No. 4,459,402 to Morris et al. and U.S. Pat. No. 4,420,607 to Morris et al. teach that 4,4'-stilbenedicarboxylic acid can be copolymerized with aliphatic diols and terephthalic acid for materials with improved flexural modulus. None of the copolymers contain a poly(ethylene glycol) monomeric portion. This monomeric portion allows the copolymer to be delivered from an aqueous medium (i.e., liquid and powder detergents, rinse cycle softeners, and dryer sheets).
Thus, there is a need in the art for copolymers which not only function as soil release agents (such as the poly(ethylene terephthalate)/poly(oxyethylene terephthalate) copolymers discussed above) but which also function as whitening agents for use in detergent compositions. Moreover, there is a need for the production of such polymers which can be delivered though an aqueous medium.
There is further a need in the art for polymers which enhance fluorescence when used to treat hydrophobic (e.g., soiled cotton, polyester, and/or blends of cotton and polyester) substrates.
Applicants have now discovered novel copolymers which have dual soil-release and whitening functions and which can be delivered through an aqueous medium such in heavy duty detergent compositions (liquid or powder), rinse cycle softeners or dryer sheets.